Process for producing reclaimed expandable polystyrene resin particle

ABSTRACT

It is possible to recover a volume reducing agent from a waste foamed polystyrene resin material compacted with the volume reducing agent and to impregnate a blowing agent into the compacted material at ordinary room temperature. The volume reducing agent is preferably a polar solvent having solubility with respect to the polystyrene resin and exhibiting a mutual solubility with the blowing agent, which is one whose hydrogen bond term δh and polarity term δp of the Hansen solubility parameters satisfy the following conditions: 
     
       
         (δ p −5.8) 2 +(δ h −4.3) 2 &lt;50 and δ p   2   +δh   2 &gt;46  [units :(J/cm 3 ) 1/2 ] 
       
     
     The solvent used as the volume reducing agent is preferably at least one solvent selected from the group consisting of ketones, esters, polyhydric alcohol ether acetates, ethers, halogenated hydrocarbons, nitro compounds, and amines. The solvent may be a mixed solvent consisting essentially of at least one solvent selected from the above-described group and at least one solvent selected from the group consisting of aliphatic hydrocarbons and aromatic hydrocarbons.

TECHNICAL FIELD

The present invention relates to a method of producing regeneratedexpandable polystyrene resin particles to regenerate and reuse expandedpolystyrene resins used as thermal and heat insulation materials,packing materials for packaging, etc. More particularly, the presentinvention relates to a method of producing regenerated expandablepolystyrene resin particles to regenerate foamed polystyrene resinmaterials discarded as waste after use, or flashes, defective products,etc. produced during the process of forming foamed materials and toreuse them as foamed materials.

BACKGROUND ART

Expanded polystyrene is used in large quantities as packing materials,cushioning materials, thermal insulation materials for buildings andrefrigerators, tatami cores, roofing, container packaging materials,decorative materials, foundry materials, and so forth. Waste of thesematerials or foamed polystyrene resin materials produced as flashes ordefective products and discarded as waste should preferably be recycledand reused as much as possible. However, expanded polystyrene is largein specific volume and bulky at sites where waste expanded polystyreneoccurs. Therefore, it is desirable in order to recycle these wasteexpanded polystyrene materials that they should be subjected to volumereduction at sites where waste expanded polystyrene occurs from theviewpoint of ensuring a space for collection and storage and reducingthe cost of transporting the waste to a regeneration factory.

Various methods for volume reduction have been proposed, e.g. a methodwherein waste expanded polystyrene is crushed and formed into blocks byfriction compression or melting under heating, and a method whereinwaste expanded polystyrene is dissolved in a solvent to achieve volumereduction. For example, Japanese Patent Application UnexaminedPublication (KOKAI) No. Sho 50-109966 discloses a method wherein styreneresin particles having a size not larger than 1 cm and a specificgravity of about 0.2 and containing a large number of cells aredispersed in water containing an organic solvent and stirred for atleast 30 minutes at a temperature not lower than the softening point ofthe resin and then impregnated with hydrocarbon to regenerate expandablestyrene resin particles. With this method, it is generally difficult tocompact foamed styrene resin articles to a specific gravity of 0.2stably and industrially.

Japanese Patent Application Unexamined Publication (KOKAI) No. Hei6-87973 proposes a method wherein styrene resin particles with a size of0.3 to 5 mm obtained by melting a compacted material of foamed styreneresin articles under heating with an extruder, a heated roll or the likeare dispersed in an aqueous medium containing an organic dispersant andimpregnated with an easily-volatile hydrocarbon at a temperature notlower than 100° C. and not higher than 140° C. to produce sphericalregenerated expandable styrene resin particles. This method requiresthat impregnation with a volatile hydrocarbon should be carried out in areaction pressure vessel, e.g. an autoclave, in order to keep pressureand temperature. It is difficult to use such equipment at a site wherewaste is produced. Moreover, the method suffers low productivity.

Japanese Patent Application Unexamined Publication (KOKAI) Nos. Hei5-310987 and Hei 11-269299 disclose a method wherein foamed styreneresin articles are heat-shrunk into blocks, which are then crushed toobtain styrene resin particles. The styrene resin particles aredispersed in an aqueous medium containing an organic polymer dispersantand impregnated with an easily-volatile blowing agent to produceregenerated expandable styrene resin particles.

However, this method uses a large amount of organic polymer dispersant.Therefore, wastewater treatment becomes a new problem. Thus, the methodinvolves a problem in terms of cost and lacks practicality. The methodrequires that impregnation with a blowing agent should be carried out ina reaction pressure vessel, e.g. an autoclave, in order to keep pressureand temperature. In addition, the method suffers low productivity.

In Japanese Patent Application Unexamined Publication (KOKAI) No. Hei5-98062, a crushed, foamed styrene resin material is melted by heatingin an extruder, extruded and cut into styrene resin particles. Thestyrene resin particles are dispersed in pure water, and a styrenemonomer solution of benzoyl peroxide is added to the dispersion, therebyallowing the styrene resin particles to absorb and polymerize with thesolution. Thereafter, the styrene resin particles are impregnated withbutane as a blowing agent.

Thus, the resin destroyed by melting on heating is ensured aweight-average molecular weight in the range of 200,000 to 400,000. Thismethod similarly uses a large amount of dispersant. Therefore,wastewater treatment becomes a new problem. Thus, the method involves aproblem in terms of cost and lacks practicality. Further, the methodrequires that polymerization should be performed in a reaction pressurevessel, e.g. an autoclave, in order to keep pressure and temperature.Therefore, the method is difficult to use at a site where waste isproduced, and suffers low productivity, as in the case of theabove-described methods.

Japanese Patent Application Unexamined Publication (KOKAI) No. Hei9-208734 states that expandable styrene resin particles obtained bysuspension polymerization, which are off-specification products havingan average particle diameter not larger than 0.4 mm or not smaller than1.3 mm, are introduced into an extruder, together with a styrene resinand a blowing agent, and the mixture is extruded into a heated liquidunder pressure and instantaneously cut to obtain regenerated expandableparticles. This method needs to carry out the process in a reactionpressure vessel, e.g. an autoclave, in order to allow the resin extrudedfrom the extruder to maintain a pressure higher than the saturated vaporpressure of the blowing agent and a necessary temperature. Accordingly,the method is difficult to use at a site where waste is produced, andsuffers low productivity, as in the case of the above-described methods.

As has been stated above, the regenerated expandable polystyrene resinparticle producing methods that have heretofore been proposed areregeneration methods which are roughly as follows. From a compactedmaterial reduced in volume with a volume reducing agent, the volumereducing agent and the polystyrene resin are separated. Alternatively,blocks of polystyrene resin are formed by heat shrinkage. Then, thepolystyrene resin is impregnated with a blowing agent to obtainregenerated expandable polystyrene resin particles.

These conventional regenerated expandable polystyrene resin particleproducing methods require that the operation for separating the volumereducing agent and the operation for impregnating the resin with theblowing agent should be performed separately from each other, and henceneed a large number of man-hours. Further, because a dispersant is used,wastewater treatment is required. Therefore, the conventional methodsare disadvantageous from the viewpoint of production cost.

Further, the conventional methods suffer from the problem of energy lossdue to heat shrinkage. The method wherein the volume reducing agent isseparated from the compacted material by heating or the polystyreneresin melted under heating is extruded by an extruder or the like forheat shrinkage to reduce the volume thereof suffers from the problem ofdeterioration of the resin due to heat history. The method whereinpolymerization is performed again to compensate for the deteriorationsuffers from the loss of energy and needs a process for polymerizationand hence requires an increasingly more complicated process. With theforegoing problems as background, the present invention was made toattain the following objects.

An object of the present invention is to provide a method of producingregenerated expandable polystyrene resin particles that is capable ofsimultaneously performing the recovery of a volume reducing agent from awaste foamed polystyrene resin material compacted with the volumereducing agent and the impregnation with a blowing agent at ordinaryroom temperature.

Another object of the present invention is to provide a method ofproducing regenerated expandable polystyrene resin particles thatconsumes minimum heat energy.

DISCLOSURE OF INVENTION

(First Method of Producing Regenerated Expandable Polystyrene ResinParticles)

A first method of producing regenerated expandable polystyrene resinparticles according to the present invention is characterized in that awaste foamed polystyrene resin material made of an expanded polystyreneresin is dissolved in a volume reducing agent having solubility withrespect to the foamed polystyrene resin material and exhibiting a mutualsolubility with a blowing agent to be used, thereby forming a compactedmaterial, and the compacted material is dipped in the blowing agent forexpanding the polystyrene resin at ordinary room temperature, therebyextracting the volume reducing agent from the compacted material and, atthe same time, impregnating the compacted material with the blowingagent to regenerate the expanded polystyrene resin, and forming theregenerated expandable polystyrene resin into a predetermined shape.

The term “polystyrene resin” as used in the present invention means apolymer obtained by polymerizing styrene or a copolymer obtained bycopolymerization of a material containing a polystyrene as a maincomponent with another monomer. The term “expanded polystyrene resin” asused in the present invention means a resin having small closed cellsproduced by impregnating the above-described polystyrene resin with ablowing agent and expanding the impregnated polystyrene resin underheating. The term “foamed polystyrene resin material” as used in thepresent invention means the above-described expanded polystyrene resinshaped by a publicly known forming method, and mainly means foamedmaterials discarded as waste after use.

Further, foamed polystyrene resin materials in the present invention maybe different from each other in the constituent material and the methodof forming according to the purpose of use and the shape thereof, suchas thermal insulation materials and packing materials, and roughlydivided into those molded from expandable polystyrene resin particles(i.e. moldings), and those expanded by extrusion (i.e. boards, styrenepaper, etc.). The expandable polystyrene resin is the above-describedpolystyrene resin containing a blowing agent, which is also used as amaterial for forming the above-described foamed polystyrene resinmaterial. The above-described expandable polystyrene resin particles areglobular or columnar beads of the above-described polystyrene resincontaining a blowing agent, which are used as a foaming material. Whenheated, the beads expand and form closed cells therein.

The volume reducing agent in the present invention is a polar solventhaving solubility with respect to the polystyrene resin and exhibiting amutual solubility with the blowing agent. Generally speaking, the polarsolvent used as the volume reducing agent in the present invention is aliquid consisting of molecules with a large dipole moment and having alarge specific dielectric constant. The polar solvent used as the volumereducing agent in the present invention should desirably be a polarsolvent whose hydrogen bond term δh and polarity term δp satisfy thefollowing conditions when specified by the Hansen solubility parameters(Hansen 3D solubility parameters):

(δp−5.8)²+(δh−4.3)²<50 and δp ² +δh ²>46  [units:(J/cm³)^(1/2)]

The range of numerical values for the polar solvent was determined byExamples and Comparative Examples (described later).

In the Hansen solubility parameters, solubility parameters introduced byHildebrand are divided into three components, i.e. a dispersion term δd,a polarity term δp, and a hydrogen bond term δh, and expressed in athree-dimensional space. The dispersion term δd shows the effect ofnon-polar interaction. The polarity term δp shows the effect ofinter-dipole force. The hydrogen bond term δh shows the effect ofhydrogen bond strength. In practical application, a two-dimensional mapof the polarity term δp and the hydrogen bond term δh is used. Thevalues of the Hansen solubility parameters have been examined for manysolvents and resins, and stated, for example, in Wesley L. Archer,“Industrial Solvents Handbook”. Regarding mixtures of solvents, theHansen solubility parameters can be calculated in terms of averagesolubility parameters according to the mixing ratio.

On a parameter map in which the polarity term δp is plotted along theabscissa axis, and the hydrogen bond term δh along the ordinate axis,polystyrene is at the position of δp=5.8 and δh=4.3 (see FIG. 1). Polarsolvents falling within a circle centered at this position and having aradius of 7.1 exhibit solubility with respect to polystyrene. Meanwhile,publicly-known, easily-volatile hydrocarbons generally used as blowingagents for polystyrene resins are located at positions near the origin(δp=δh=0) on the parameter map.

Accordingly, solvents located at short distances from the origin definedby the Hansen solubility parameters can be said to exhibit a high mutualsolubility with blowing agents (in general, easily-volatilehydrocarbons). When a compacted material formed by mixing together apolystyrene resin and a volume reducing agent is dipped in a blowingagent, the volume reducing agent in the compacted material diffuses intothe blowing agent until an equilibrium is reached, and the blowing agentpenetrates into the compacted material. The expandable polystyrene resinregeneration treatment according to the present invention ischaracterized in that the volume reducing agent in the compactedmaterial is diffused into the blowing agent until the volume reducingagent in the compacted material and the blowing agent reach anequilibrium at ordinary room temperature. That is, the regenerationtreatment is characterized by allowing the blowing agent to penetrateinto the compacted material, which is a mixture of the volume reducingagent and the polystyrene resin swollen with the volume reducing agent,at ordinary room temperature.

Therefore, the expandable polystyrene resin regeneration treatmentaccording to the present invention also features minimum energy loss andhence allows blowing agent penetration equipment to be minimized inscale. When a polar solvent exhibiting a high mutual solubility with theblowing agent is used as a volume reducing agent, the rate at which thevolume reducing agent in the compacted material diffuses into theblowing agent is high. Consequently, the compacted material loses thevolume reducing agent rapidly to become a solid resin. In other words,the penetration of the blowing agent is retarded, so that an extremelylong time is required for the expandable polystyrene resin regenerationtreatment performed at ordinary room temperature. From the practicalpoint of view, the expandable polystyrene resin regeneration shouldpreferably be carried out in such a way that the volume reducing agentin the compacted material gradually diffuses into the blowing agent in ashort period of time, and the blowing agent is allowed to penetrate intothe resin swollen with the volume reducing agent by dipping.

The term “volume reducing agent” as used in the present invention meansas follows. On a Hansen solubility parameter map in which the polarityterm δp is plotted along the abscissa axis, and the hydrogen bond termδh along the ordinate axis, polystyrene is at the position of δp=5.8 andδh=4.3 (see FIG. 1). Polar solvents falling within a circle centered atthis position and having a radius of 7.1 exhibit solubility with respectto polystyrene (i.e. within the region A in FIG. 1). Specific examplesof polar solvents satisfying these conditions and hence usable as thevolume reducing agent in the present invention are ketones, esters,polyhydric alcohol ether acetates, ethers, halogenated hydrocarbons,nitro compounds, and amines. At least one selected from the groupconsisting of such solvents in which a polystyrene resin is readilysoluble is usable as a volume reducing agent, either alone or as amixture.

However, aliphatic hydrocarbons, e.g. paraffin, olefin and acetylenichydrocarbons, and aromatic compounds that are carbocyclic compoundshaving a benzene nucleus, e.g. benzene, toluene, and xylene, cannot beused alone (singly) as a volume reducing agent in the present invention.Such aliphatic hydrocarbons and aromatic compounds are at shortdistances from the origin defined by the Hansen solubility parametersand hence exhibit a high mutual solubility with the blowing agent(easily-volatile hydrocarbon). Accordingly, if any of these compoundshaving a high mutual solubility is used as a volume reducing agent, thevolume reducing agent in the compacted material diffuses into theblowing agent at a high rate. Consequently, the compacted material losesthe volume reducing agent rapidly to become a solid polystyrene resin.

Therefore, solvents that are within 6.8 from the origin on the Hansensolubility parameter map are excluded from the group of solvents usableas the volume reducing agent in the present invention (i.e. those withinthe region B in FIG. 1). Further, alcohols and polyhydric alcohols fallwithin the region C on the Hansen solubility parameter map (see FIG. 1)and cannot be used alone as a volume reducing agent. Thus, solventsfalling within the region A on the Hansen solubility parameter map areusable alone in the present invention. If a mixed solvent is used,solvents falling within the regions A, B and C on the Hansen solubilityparameter map should be mixed together as follows. Solvents fallingwithin the regions A and B, respectively, are mixed together to preparea mixed solvent. Solvents falling within the regions A and C,respectively, are mixed together to prepare a mixed solvent. Solventsfalling within the regions B and C, respectively, are mixed together toprepare a composition serving as a solvent falling within the region A.

Regarding volume reducing agents comprising compositions prepared bymixing together solvents as stated above, polar solvents falling withinthe above-described circle having a radius of 7.1 exhibit solubilitywith respect to polystyrene (i.e. within the region A in FIG. 1). Morespecifically, the following solvents are used either alone or as amixture of two or more:

Nitrobenzene, o-dichlorobenzene, acetophenone, 1,2-dichloroethane,tetrachloroethylene, 1,1-dichloroethylene, 1,1-dicholoroethane,quinoline, pyridine, ethyl cinnamate, methylene chloride, 1,4-dioxane,aniline, morpholine, N-methylmorpholine, N-ethylmorpholine,cyclohexanone, 1,1,2,2-tetrachloroethane, diethyl carbonate, dimethylphthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate,anisole, benzonitrile, 1-nitropropane, propylene glycol phenyl ether,propylene glycol hexyl ether, dipropylene glycol butyl ether,dipropylene glycol hexyl ether, triethylene glycol dimethyl ether,triethylene glycol ethyl ether, triethylene glycol butyl ether,triethylene glycol propyl ether, ethylene glycol hexyl ether, diethyleneglycol dimethyl ether, diethylene glycol butyl ether, butylene glycolbutyl ether, cyclohexylamine, ethylene glycol ethyl ether acetate,ethylene glycol butyl ether acetate, propylene glycol methyl etheracetate, diethylene glycol butyl ether acetate, dipropylene glycolmethyl ether acetate, tetrahydrofuran, dimethyl succinate, dimethylglutarate, dimethyl adipate, diethyl succinate, isophorone, methylacetate, ethyl acetate, propyl acetate, isopropyl acetate, butylacetate, isobutyl acetate, amyl acetate, methyl isoamyl ketone, methylethyl ketone, diethyl ketone, methyl propyl ketone, methyl isobutylketone, and methyl hexyl ketone.

The compacted waste expanded polystyrene resin has been swollen by thedissolving action of the volume reducing agent. The compacted materialis dipped in the blowing agent. The volume reducing agent in thecompacted material is extracted into the blowing agent. In other words,the volume reducing agent in the compacted material diffuses into theblowing agent until an equilibrium is reached, and the blowing agentpenetrates into the compacted material.

Accordingly, the polystyrene resin can be impregnated with the blowingagent at the same time as the volume reducing agent is extracted fromthe compacted material. The term “blowing agent” as used in the presentinvention means an easily-volatile hydrocarbon. Butane, pentane, hexane,etc. and isomers thereof may be used either alone or as a mixture of twoor more. However, when butane, which is gas under ordinary temperatureand pressure conditions, is used as a blowing agent, it needs to behandled in a liquid state under a pressure not lower than 0.11 MPa(gauge pressure) when the treatment temperature is 20° C. Therefore, asimple pressure vessel of 0.5 MPa (gauge pressure) or below is used.

After the compacted material has been dipped in or kneaded with theblowing agent, it is allowed to stand, thereby separating the solidmatter from the mixed liquid consisting essentially of the volumereducing agent and the blowing agent. The remaining mixed liquid isseparated by a distillation operation to recover the volume reducingagent and the blowing agent for reuse. The compacted material preparedby the above-described method is a viscous substance comprising thepolystyrene resin swollen and dissolved in the volume reducing agent. Itis necessary to obtain, from this substance, regenerated expandablepolystyrene resin particles with a diameter of 0.5 to 1.5 mm generallyused in the expanded bead foaming process. Because the compactedmaterial is a viscous substance, it is necessary to form regeneratedexpandable polystyrene resin particles with the above-described particlediameter while preventing the polystyrene resin particles from adhering(fusing) together.

One method available for this purpose is as follows. The compactedmaterial is extruded in the form of a string at room temperature, andthis is held on a non-adhesive substrate of polyethylene, fluorocarbonresin, or the like. The string-shaped, compacted material held on thesubstrate is dipped in the above-described blowing agent at atemperature at least 20° C. lower than the softening temperature of thepolystyrene resin, preferably at a mild temperature of 10 to 40° C.,thereby performing the extraction of the volume reducing agent and theimpregnation with the blowing agent. Thereafter, the string-shaped,compacted material is cut into particles with a desired shape.

(Second Method of Producing Regenerated Expandable Polystyrene ResinParticles)

A second method of producing regenerated expandable polystyrene resinparticles according to the present invention is characterized in that awaste foamed polystyrene resin material made of an expanded polystyreneresin is dissolved in a volume reducing agent having solubility withrespect to the foamed polystyrene resin material and exhibiting a mutualsolubility with a blowing agent to be used, thereby forming a compactedmaterial, and the compacted material and an extraction solvent forextracting the volume reducing agent are dispersed and kneaded with eachother to extract the volume reducing agent, thereby forming a solidmaterial. Then, the solid material is formed into a particulate materialconsisting of particles and dipped in the blowing agent for expandingthe polystyrene resin at ordinary room temperature, and, at the sametime, the volume reducing agent is further extracted to regenerate theexpanded polystyrene resin.

The second method of producing regenerated expandable polystyrene resinparticles according to the present invention is substantially the sameas the above up to the step of dissolving a waste expanded polystyreneresin in a volume reducing agent to form a compacted material. Thecompacted material, which is a viscous substance, and an extractionsolvent are kneaded together in a stirring machine to mix together theextraction solvent and the compacted material uniformly. As the resultof kneading together the compacted material and the extraction solvent,the volume reducing agent in the compacted material diffuses into theextraction solvent phase. Thus, the volume reducing agent in thecompacted material is extracted. In other words, the volume reducingagent in the expanded polystyrene resin is extracted to reduce thecontent of the volume reducing agent.

The process of kneading together the compacted material and theextraction solvent is carried out as a pretreatment for impregnation ofthe blowing agent into the compacted material. The compacted material isstirred, together with the extraction solvent, in a homogenizer or thelike to effect dispersion. Alternatively, the compacted material and theextraction solvent are kneaded together at room temperature by using amixer or the like. Thereafter, the mixture is allowed to stand, and thecompacted material is taken out. Accordingly, it is possible to performa treatment for minimizing the content of the volume reducing agent andfor reducing the adhesion of the compacted material due to the viscositythereof.

As the extraction solvent used in the pretreatment, it is possible touse one selected from easily-volatile hydrocarbons usable as blowingagents, and alcohols and polyhydric alcohols exhibiting a low solubilitywith respect to the polystyrene resin. The compacted material thusobtained, which is a solid material, is extruded at room temperature byusing an extruder and cut into particles.

In the second method of the present invention, the shaped compactedmaterial is dipped in the blowing agent at a temperature at least 20° C.lower than the softening temperature of the polystyrene resin,preferably at a mild temperature of 10 to 40° C., thereby performing theextraction of the volume reducing agent and the impregnation with theblowing agent in the same way as in the above-described first method ofthe present invention.

As has been detailed above, an advantage of the present invention is asfollows. A compacted material obtained by reducing the volume of a wastefoamed polystyrene resin material with a volume reducing agent is dippedin a blowing agent to extract the volume reducing agent and to performimpregnation with the blowing agent, thereby producing regeneratedexpandable polystyrene resin particles. Therefore, the operation forrecovery of the volume reducing agent and the operation of impregnatingthe blowing agent into the resin can be performed in a single processstep.

Accordingly, it is possible to simplify the process in comparison to theconventional post-impregnation method and to save heat energy. Anotheradvantage of the present invention is as follows. It is unnecessary tocarry out heating at a temperature not lower than the meltingtemperature of the resin during the process. Accordingly, deteriorationof the regenerated resin due to heat history is minimized. Moreover, theblowing agent used to extract the volume reducing agent can be separatedby a distillation operation to recover the volume reducing agent and theblowing agent for reuse. Accordingly, the method of the presentinvention is free from environmental pollution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a Hansen solubility parameter map in which the polarity termδp is plotted along the abscissa axis, and the hydrogen bond term δhalong the ordinate axis.

FIG. 2 is a diagram schematically showing an embodiment 1 of the methodof producing regenerated expandable polystyrene resin particlesaccording to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1)

FIG. 2 is a diagram schematically showing an embodiment 1 of the methodof producing regenerated expandable polystyrene resin particlesaccording to the present invention. A waste foamed polystyrene resinmaterial is crushed, if necessary, and sprayed with or introduced into avolume reducing agent, thereby dissolving 100 parts (phr, parts byweight) of the waste foamed polystyrene resin material in 100 to 200parts of the volume reducing agent. Foreign substances, such as metalpieces, in the compacted material dissolved in the volume reducing agentare removed by a method, e.g. filtration, or magnetic adhesion usingmagnets. Next, the compacted material is shaped into a string-like formby a forming machine, e.g. a plunger extruder or a screw extruder, atroom temperature.

Prior to the shaping process, the viscosity of the compacted material isadjusted according to need. It is preferable that the volume reducingagent content should be adjusted to be 10 to 150 parts (parts by weight)with respect to 100 parts of the foamed polystyrene resin material byextracting the volume reducing agent or adding the foamed polystyreneresin material or the volume reducing agent.

Because it is a viscous string-shaped substance, the shaped compactedmaterial is held by being wound around a non-adhesive plate- orbar-shaped substrate of polyethylene, fluorocarbon resin, etc. Thestring-shaped, compacted material held on the substrate is dipped in aneasily-volatile hydrocarbon blowing agent, e.g. butane, pentane, orhexane, which is used as a blowing agent, thereby performing anextraction and impregnation treatment. The dipping of the compactedmaterial in the blowing agent is carried out at ordinary roomtemperature. However, when butane, which is gas under ordinarytemperature and pressure conditions, is used as a blowing agent, itneeds to be handled in a liquid state under a pressure not lower than0.11 MPa (gauge pressure) when the treatment temperature is 20° C.Therefore, a simple pressure vessel of 0.5 MPa (gauge pressure) or belowis used.

The mixed liquid after the dipping treatment is separated to recover thevolume reducing agent and the blowing agent for reuse by distillationusing the difference in boiling point between them or by gas-liquidseparation. In gas-liquid separation, the mixed liquid is introducedinto a flash drum kept at a lower pressure than the dipping pressure tovaporize only the blowing agent, thereby separating and recovering thevolume reducing agent from the mixture. The vaporized blowing agent isrecondensed by cooling under pressure for reuse. The operation ofseparating and recovering the volume reducing agent and the blowingagent may be carried out as a treatment of the mixed liquid after thedipping treatment. Alternatively, the separating and recoveringoperation may be performed continuously during the dipping treatment torenew the blowing agent. Therefore, the volume reducing agent and theblowing agent can be recycled without being released into theenvironment.

After being dipped for a predetermined period of time, thestring-shaped, compacted material is cut by a cutting machine, e.g. astrand cutter, to obtain regenerated expandable polystyrene resinparticles. It is preferable that the blowing agent content should be 6to 10 parts (parts by weight) with respect to 100 parts of thepolystyrene resin.

(Embodiment 2)

A waste foamed polystyrene resin material is crushed, if necessary, andsprayed with or introduced into a volume reducing agent, therebydissolving the waste foamed polystyrene resin material in the volumereducing agent to form a compacted material. Up to this step, theembodiment 2 is the same as the embodiment 1. The embodiment 2 isdistinguished by having the step of dispersing and kneading together thecompacted material and an extraction solvent for extracting the volumereducing agent as a step subsequent to the above-described step.

As the extraction solvent, it is possible to use one selected fromeasily-volatile hydrocarbons usable as blowing agents, and alcohols andpolyhydric alcohols exhibiting a low solubility with respect to thepolystyrene resin. Thus, the compacted material is reduced in the volumereducing agent content to form a solid material. The solid material isformed into a particulate material consisting of particles with adiameter of 0.5 to 1.5 mm by a forming machine. A preferable volumereducing agent content in the particulate material is 10 to 100 parts(parts by weight) with respect to 100 parts of the polystyrene resin.

The particulate material is dipped in a blowing agent for expanding thepolystyrene resin for about 12 to 48 hours at ordinary room temperature,and, at the same time, the volume reducing agent is further extracted toregenerate an expandable polystyrene resin. It is preferable that theblowing agent content should be 6 to 10 parts (parts by weight) withrespect to 100 parts of the polystyrene resin. The mixed liquid afterthe dipping treatment is recovered and reused in the same way as in theembodiment 1. The separating and recovering operation can also beperformed to renew the blowing agent during the dipping treatment as inthe case of the embodiment 1.

EXAMPLES

The present invention will be described below by way of examples.

Examples 1 to 8 and Comparative Examples 1 to 4

7 g of bead expanded polystyrene with an expansion ratio of 40 was cutinto a square column 10 mm×10 mm×50 mm in size. This was introduced into10 g of each volume reducing agent shown in Table 1 below and dissolvedtherein at room temperature to form a compacted material. The compactedmaterial was extruded in the form of a string with a diameter of 2 mm bya plunger extruder. The string-shaped compacted material was spirallywound around a low-density polyethylene tube with an outer diameter of 5mm and dipped in 10 ml of n-hexane.

After 4 hours had elapsed, the string-shaped compacted material wasremoved from the tube and further dipped in the n-hexane for 16 hours atordinary room temperature (about 20° C.). Then, the string-shapedcompacted material was taken out of the n-hexane and cut into particlesthat were 1 mm in size. After the expandable resin particles had beenallowed to stand for 6 hours, a foaming test was carried out in boilingwater for 1 minute. Table 1 shows the properties of the compactedmaterials and the results of the foaming test performed on theexpandable resin particles.

It should be noted that the volume reduction time was measured asfollows. A bead expanded polystyrene molded material with an expansionratio of 50 was cut into a cube 10 by 10 mm square to prepare aspecimen. This was introduced into 50 g of each volume reducing agentshown in Table 1 below at a liquid temperature of 20° C., and sunk inthe liquid with a glass rod to measure the time required for thespecimen to break down and to disperse or dissolve in the volumereducing agent. It was possible to deduce the following numerical valuesfrom the analysis of these examples and comparative examples. That is,solvents used in the present invention are those whose hydrogen bondterm δh and polarity term δp of the Hansen solubility parameters satisfythe following conditions:

(δp−5.8)²+(δh−4.3)²<50 and δp ² +δh ²>46  [units:(J/cm³)^(1/2)]

Solvents satisfying the above conditions in the present invention weredetermined as follows.

The value “46” was deduced from the experimental results regardingdipropylene glycol monomethyl ether acetate (abbreviated as “DPMA”) inExample 7. Regarding DPMA, δp²+δh²=46.6. This is the smallest (δp²+δh²)value of those of solvents usable as a volume reducing agent in examplesof the present invention. From the experimental results, the conditionof δp²+δh²>46 was set in the present invention. That is, ordinary beadexpanded polystyrene foams are products with an expansion ratio of 5 to100, and the expansion ratio of DPMA is 5. Therefore, this is defined asa region A.

Another condition, i.e. (δp−5.8)²+(δh−4.3)²<50, was set as follows.Among solvents providing good volume reduction conditions, limonene inComparative Example 2 exhibited the largest [(δp−5.8)²+(δh−4.3)²] value(45.5). Among solvents inferior in volume reduction performance,dipropylene glycol monomethyl ether (abbreviated as “DPM”) inComparative Example 4 exhibited the smallest [(δp−4.3)²+(δh−2.1)²] value(55.1). An intermediate value between the two values was defined as aboundary value “50 ”.

Example 9

To a compacted material prepared in the same way as in Example 8,n-hexane was added in an amount half of the amount of the compactedmaterial. The mixture was kneaded for 1 minute at room temperature(about 20° C.) in a mixer. The same operation was repeated twice withthe liquid portion renewed. The compacted material changed from beingtransparent to white and semitransparent, and its adhesion reduced. Thecompacted material was extruded in the form of a string by a plungerextruder and cut into particles with a diameter of 1 mm by a strandcutter. Thereafter, the particulate material was dipped in n-pentane.The dipping treatment was performed for 20 hours at room temperature.Then, a foaming test was carried out. As a result, substantiallyspherical expandable resin particles with an expansion ratio of 49 wereobtained.

TABLE 1 Appearance Classi- Volume reducing agents Volume Volume of fica-(solubility parameters reduction reduction compacted Expansion tion δp,δh) condition time material ratio Ex. 1 acetone (10.4, 7.0) good 2 sec.transparent 7 two layers Ex. 2 tetrahydrofuran good 8 sec. transparent 7(5.7, 8.0) uniform Ex. 3 ethyl acetate good 5 sec. transparent 12 (5.3,7.2) uniform Ex. 4 propylene glycol good 14 sec. transparent 17monomethyl ether uniform acetate (6.1, 6.6) Ex. 5 ethylene glycol good11 sec. transparent 18 monoethyl ether acetate uniform (4.7, 10.6) Ex. 6ethylene glycol mono-n- good 17 sec. transparent 16 butyl ether acetateuniform (6.1, 10.0) Ex. 7 dipropylene glycol good 70 sec. transparent 5monomethyl ether uniform acetate (5.3, 4.3) Ex. 8 adipic, glutaric andgood 50 sec. transparent 47 succinic acid dimethyl uniform estercomposition (4.7, 9.8) Comp. xylene good 8 sec. transparent 1.4 Ex. 1(1.8, 2.5) uniform Comp. limonene good 30 sec. transparent 1.0 Ex. 2(0.6, 0.0) uniform Comp. tripropylene glycol slow more than white 1.3Ex. 3 methyl ether 40 min. two layers (3.5, 11.5) Comp. dipropyleneglycol slow more than white 3 Ex. 4 monomethyl ether 25 min. two layers(4.0, 11.5)

INDUSTRIAL APPLICABILITY

Regenerated expandable polystyrene resin particles produced by thepresent invention are usable as a high-quality material for foamingcontainer packaging materials, e.g. packing materials and cushioningmaterials, and so forth.

What is claimed is:
 1. A method of producing regenerated expandablepolystyrene resin particles, comprising the steps of: dissolving a wastefoamed polystyrene resin material made of an expanded polystyrene resinin a volume reducing agent having solubility with respect to said foamedpolystyrene resin material and exhibiting a mutual solubility with ablowing agent to be used, thereby forming a compacted material; dippingsaid compacted material in said blowing agent for expanding saidpolystyrene resin at ordinary room temperature, thereby extracting saidvolume reducing agent from said compacted material and, at the sametime, impregnating said compacted material with said blowing agent toregenerate said expanded polystyrene resin; and forming said expandedpolystyrene resin regenerated into a predetermined shape.
 2. A method ofproducing regenerated expandable polystyrene resin particles, comprisingthe steps of: dissolving a waste foamed polystyrene resin material madeof an expanded polystyrene resin in a volume reducing agent havingsolubility with respect to said foamed polystyrene resin material andexhibiting a mutual solubility with a blowing agent to be used, therebyforming a compacted material; dispersing and kneading together saidcompacted material and an extraction solvent for extracting said volumereducing agent to extract said volume reducing agent, thereby forming asolid material; forming said solid material into a particulate materialconsisting of particles; and dipping said particulate material in theblowing agent for expanding said polystyrene resin at ordinary roomtemperature, and, at the same time, further extracting said volumereducing agent to regenerate said expanded polystyrene resin.
 3. Amethod of producing regenerated expandable polystyrene resin particlesaccording to claim 1 or 2, wherein said compacted material is dipped insaid blowing agent at a temperature at least 20° C. lower than asoftening temperature of said polystyrene resin, thereby performingextraction of said volume reducing agent and impregnation with saidblowing agent.
 4. A method of producing regenerated expandablepolystyrene resin particles according to claim 3, wherein said blowingagent is at a temperature of 10 to 40° C.
 5. A method of producingregenerated expandable polystyrene resin particles according to oneselected from claims 1 or 2, wherein said volume reducing agent is apolar solvent having solubility with respect to said polystyrene resinand exhibiting a mutual solubility with said blowing agent, said polarsolvent being one whose hydrogen bond term δh and polarity term δofHansen solubility parameters satisfy the following conditions:(δp−5.8)²+(δh−4.3)²<50 and δp ² +δh ²>46  [units:(J/cm³)^(1/2)]
 6. Amethod of producing regenerated expandable polystyrene resin particlesaccording to claim 5, wherein the solvent used as said volume reducingagent is at least one solvent selected from the group consisting ofketones, esters, polyhydric alcohol ether acetates, ethers, halogenatedhydrocarbons, nitro compounds, and amines.
 7. A method of producingregenerated expandable polystyrene resin particles according to claim 5,wherein the solvent used as said volume reducing agent is a mixedsolvent consisting essentially of at least one solvent selected from thegroup consisting of aliphatic hydrocarbons and aromatic hydrocarbons,and at least one solvent selected from the group consisting of ketones,esters, polyhydric alcohol ether acetates, ethers, halogenatedhydrocarbons, nitro compounds, and amines.
 8. A method of producingregenerated expandable polystyrene resin particles according to claim 5,wherein the solvent used as said volume reducing agent is a mixedsolvent consisting essentially of at least one solvent selected from thegroup consisting of aliphatic hydrocarbons and aromatic hydrocarbons,and at least one solvent selected from the group consisting of alcoholsand polyhydric alcohols.
 9. A method of producing regenerated expandablepolystyrene resin particles according to claim 5, wherein the solventused as said volume reducing agent is a mixed solvent consistingessentially of at least one solvent selected from the group consistingof ketones, esters, polyhydric alcohol ether acetates, ethers,halogenated hydrocarbons, nitro compounds, and amines, and at least onesolvent selected from the group consisting of alcohols and polyhydricalcohols.
 10. A method of producing regenerated expandable polystyreneresin particles according to claim 5, wherein said volume reducing agentis at least one selected from the group consisting of nitrobenzene,o-dichlorobenzene, acetophenone, 1,2-dichloroethane,tetrachloroethylene, 1,1-dichloroethylene, 1,1-dicholoroethane,quinoline, pyridine, ethyl cinnamate, methylene chloride, 1,4-dioxane,aniline, morpholine, N-methylmorpholine, N-ethylmorpholine,cyclohexanone, 1,1,2,2-tetrachloroethane, diethyl carbonate, dimethylphthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate,anisole, benzonitrile, 1-nitropropane, propylene glycol phenyl ether,propylene glycol hexyl ether, dipropylene glycol butyl ether,dipropylene glycol hexyl ether, triethylene glycol dimethyl ether,triethylene glycol ethyl ether, triethylene glycol butyl ether,triethylene glycol propyl ether, ethylene glycol hexyl ether, diethyleneglycol dimethyl ether, diethylene glycol butyl ether, butylene glycolbutyl ether, cyclohexylamine, ethylene glycol ethyl ether acetate,ethylene glycol butyl ether acetate, propylene glycol methyl etheracetate, diethylene glycol butyl ether acetate, dipropylene glycolmethyl ether acetate, tetrahydrofuran, dimethyl succinate, dimethylglutarate, dimethyl adipate, diethyl succinate, isophorone, methylacetate, ethyl acetate, propyl acetate, isopropyl acetate, butylacetate, isobutyl acetate, amyl acetate, acetone, methyl isoamyl ketone,methyl ethyl ketone, diethyl ketone, methyl propyl ketone, methylisobutyl ketone, and methyl hexyl ketone.
 11. A method of producingregenerated expandable polystyrene resin particles, comprising the stepsof: dissolving a waste foamed material made of an expanded polystyreneresin in a volume reducing agent having solubility with respect to saidfoamed polystyrene resin material and exhibiting a mutual solubilitywith a blowing agent to be used, thereby forming a compacted material;extruding said compacted material in a string-like form at roomtemperature; holding said compacted material extruded in saidstring-like form on a non-adhesive substrate for preventing adhesion ofsaid compacted material; and dipping said compacted material held onsaid substrate in said blowing agent at a temperature at least 20° C.lower than a softening temperature of said polystyrene resin, therebyperforming extraction of said volume reducing agent and impregnationwith said blowing agent.
 12. A method of producing regeneratedexpandable polystyrene resin particles, comprising the steps of:dissolving a waste foamed material made of an expanded polystyrene resinin a volume reducing agent having solubility with respect to said foamedpolystyrene resin material and exhibiting a mutual solubility with alater-mentioned blowing agent to form a compacted material; dispersingand kneading together said compacted material and an extraction solventunder stirring, thereby forming a solid material having reducedadhesion; forming said solid material into a particulate material atroom temperature; and dipping said particulate material in said blowingagent at a temperature at least 20° C. lower than a softeningtemperature of said polystyrene resin, thereby performing extraction ofsaid volume reducing agent and impregnation with said blowing agent. 13.A method of producing regenerated expandable polystyrene resin particlesaccording to claim 11 or 12, wherein said blowing agent is at atemperature of 10 to 40° C.